The present invention relates to a hydraulic control system for automatically adjusting the travel speed of a machine to the work conditions being encountered by an attached powered implement. More particularly, the present invention relates to a tractor hydraulic system which is responsive to the load imposed on the tractor by a ground-engaging implement to control the ground speed of the tractor in accordance with such load.
It is conventional to provide a hydrostatically operated earth-working machine having separate hydraulic systems, one for powering the ground drive and another for powering the implement attachment. The operator manually adjusts the ground speed of the machine depending upon the load resistance being encountered by the implement. This manual correlation between ground speed and implement load is intended to maintain a constant load on the machine and thereby provide optimum engine efficiency.
A problem with known hydraulically operated tractor-implement systems is that the operator must constantly monitor the load conditions of the implement and simultaneously adjust the ground speed in response thereto. In practice, it is nearly impossible for the operator to maintain optimum engine efficiency and still perform the other operations required of him in running the machine.
For example, in a known hydrostatically operated trencher, a trenching boom is mounted to the tractor and one hydraulic system powers the digging chain on the boom while another hydraulic system controls ground speed, forward and reverse movement, turning, and braking. If the powered digging chain suddenly encounters a rocky soil condition, the operator must slow the tractor until the higher pressure developed in the trencher hydraulic circuit, due to the increased load, is reduced either by the trencher passing through the area or by some operator action. At the same time the operator is attempting to maintain maximum tractor engine efficiency, he must steer the unit and perform other normal running operations. Thus, there has been a need for a hydraulic control system which automatically adjusts the travel speed of the tractor in response to the work conditions being encountered by the attached powered implement.
Conventional manual controls for correlating tractor ground speed with implement load conditions are ineffective in maintaining high engine efficiency because it is not always possible for the operator to give his undivided attention to monitoring the implement load and ground speed variables. Thus, the disadvantages of the present hydrostatically operated earth working machines have resulted in the hydraulic control system of the present invention which effectively reduces required operator participation and results in greater output because the tractor engine operates substantially at optimum efficiency.